RESTRICTED FRINGING REEF DEVELOPMENT ON THE SOUTHEAST FLORIDA CONTINENTAL REEF TRACT DURING THE LATE HOLOCENE

The relict Holocene reef tract offshore southeast Florida documents the near-continuous development of Acropora-dominated coral reefs throughout the Holocene. Previous studies suggest that significant reef-building in southeast Florida ceased on the inner reef at ~5830 cal B.P., potentially in response to cooling temperatures following the Holocene Thermal Maximum (HTM) (~10–5 ka). However, recent evidence from subfossil coral deposits offshore Broward County indicates that acroporid reef growth reinitiated inshore of the relict reef tract after the HTM. To constrain the spatial extent and timing of reef development at this location, we used a combination of LiDAR bathymetry, field surveys, and uranium-series dating of subfossil corals. Results from bathymetry and field surveys indicate that reef development was patchy and spatially restricted to a 4.5 km² area situated 450 to 550 m seaward of the modern shoreline. Uranium-series dating of 22 subfossil Acropora palmata, Pseudodiploria strigosa, Colpophyllia natans, and Orbicella annularis samples yielded ages between 975±6 and 3219±6 years B.P. with significant clusters centered around 3100 and 2400 years B.P. Estimated paleodepths calculated using subfossil coral age-depth data combined with established regional sea-level curves yielded minimum water depths between -0.5 and -2.1 m mean sea level (MSL). These results suggest that despite regional climatic cooling relative to the HTM, favorable conditions for shallow-water reef growth returned to southeast Florida during the late Holocene. However, based on the relatively limited spatial extent and lack of significant vertical accretion, reef growth at this site was likely restricted by factors associated with early shelf flooding, such as increased sedimentation and limited accommodation space.